The present invention relates generally to well casing fill apparatus and methods, and more particularly, to such an apparatus having a floating plate back pressure valve therein.
In the construction of oil and gas wells, a well bore is drilled into one or more subterranean formations or zones containing oil and/or gas to be produced. In most instances, after the well bore is drilled, the drill string is removed and a string of casing is run into the well bore while maintaining sufficient drilling fluid in the well bore to prevent blowouts. The term “casing string” is used herein to mean any string of pipe which is lowered into and cemented in a well bore including, but not limited to, surface casing, liners and the like.
During casing running operations, the casing string must be kept filled with fluid to prevent excessive fluid pressure differentials across the casing string and to prevent blowouts. In the past, fluid was added to the casing string at the surface after each additional casing joint was connected to the string and lowered into the well bore. Alternatively, casing fill apparatus have been utilized at or near the bottom end of the casing string to allow well fluids to enter the interior of the casing string as it is run down the well bore.
While these casing fill apparatus have been used successfully, they are relatively complex and have certain limitations. Generally, most of the prior devices include a spring-loaded, poppet-style back pressure valve which is used after the casing is positioned in the well bore to allow fluid to be pumped downwardly through the casing string while preventing reverse flow. In order to fill the casing string as it is run into the well bore, the back pressure valve must be held in an open position until the string reaches the desired location in the well bore. Typically, a shearable member holds the valve open and then is sheared when it is desired to use the valve. Not only does this arrangement require a number of precise parts, but the shearing of the shearable member requires an additional step in the process. The cost of these prior casing fill apparatus is not insignificant.
There is a need, therefore, for a casing fill apparatus that is more simple in construction and which allows filling of the casing string while running it in but does not require the step of shearing a shearable member to allow the device to operate as a back pressure valve once in the desired operating position. The present invention solves these problems by providing a simple moving or floating plate which cooperates with a stationary plate to allow flow in one direction but prevent undesired reverse flow. It also still allows the casing string to fill while running it into the well bore.